Source Code)
void __fastcall ExecuteScript(TCppWebBrowser* pCppWebBrowser, WideString wstrLang, WideString wstrScript)
{
    HRESULT hr;
    VARIANT vResult;

    IDispatch* pDocument;
    IHTMLDocument2* pHTMLDocument;
    IHTMLWindow2* pHTMLWindow;

    pDocument = pCppWebBrowser->Document;

    hr = pDocument->QueryInterface(IID_IHTMLDocument2, (void**)&pHTMLDocument);

    if(hr == S_OK)
    {
        hr = pHTMLDocument->get_parentWindow(&pHTMLWindow);

        if(hr == S_OK)
        {
            pHTMLWindow->execScript(wstrScript, wstrLang, &vResult);
            pHTMLWindow->Release();
        }

        pHTMLDocument->Release();
    }

    pDocument->Release();
}

Example)
//야후에서 이글루스 단어 검색

WideString wstrScript;
//야후 접속
CppWebBrowser1->Navigate(TVariant("http://yahoo.co.kr"));

//스크립트 날리기
wstrScript = "document.search.p.value = '이글루스';\r\ndocument.search.action = 'http://kr.rd.yahoo.com/home-dosearch/*http://kr.search.yahoo.com/search';\r\ndocument.search.submit()";

ExecuteScript(CppWebBrowser1, "JavaScript", wstrScript);